Amino-terminated SiO2 aerogel towards highly-effective lead (II) adsorbent via the ambient drying process

• First demonstration of amino-modified SiO2 aerogel via ambient drying process.
• APTES/SiO2 molar ratio had significant effects on the pore structures.
• The maximum adsorption capacity of 407.04 mg/g for Pb2 + was achieved.
• Removal percentage > 80% for 10 ppm Pb2 + after 5 cycles in a rapid adsorption test.

This work demonstrated a low-cost sol-gel and ambient drying process towards amino-modified SiO2 (SiO2-NH2) aerogels powders possessing high potential in recovering lead (II) ions from waste water, using industrial waterglass and 3-aminopropyl triethoxysilane (APTES) as the starting materials. Effects of the APTES/SiO2 molar ratio on the chemical composition and pore structure of SiO2-NH2 aerogel were investigated, and the Pb2 + adsorption properties were examined using the batch method. Results showed that the SiO2-NH2 aerogels via the ambient drying route possessed the BET surface area of 400–470 m2/g, pore volume of 1.4–1.8 ml/g, and average pore diameter of 12–16 nm. FTIR and chemical composition analysis confirmed the successful anchoring of the NH2 groups on the surface of SiO2 nanoparticles and the optimal APTES/SiO2 molar ratio was 0.21. The adsorption test showed that, at pH range of 4.0–6.0 and room temperature, the samples with the optimal APTES/SiO2 molar ratio of 0.21 exhibited relatively high adsorption capacity compared with the pure SiO2 aerogel and SiO2-NH2 aerogels with lower APTES/SiO2 molar ratio. An equilibrium adsorption time of 7 h was observed, fitting well with the pseudo-second-order kinetic model, indicating that the chelating reaction between Pb2 + and anchored NH2 group was the rate-limiting step. The adsorption isotherm was well fitted by the Langmuir adsorption model, with the maximum adsorption capacity of 407.04 mg/g. The rapid adsorption test simulating the filter membrane with SiO2-NH2 aerogel adsorbent indicated the removal percentage of higher than 80% after 5 cycles.